1. Field of the Invention
This invention relates generally to the field of power supplies, and, in particular, to standby mode power supplies for television receivers.
2. Background Information
In a conventional power supply arrangement for a video display apparatus, a primary winding of a standby transformer is coupled to the AC mains. A transformed voltage across a secondary winding of the standby transformer is full-wave rectified and is regulated by some form of linear regulation to provide power for the video display apparatus in a standby mode of operation. This standby power supply consumes power as long as the video display apparatus is connected to the AC mains, and thus also consumes power during the run mode of operation.
A main, or run mode, power supply may have a control circuit which is responsive to a decoded on/off signal to energize the run mode power supply during the run mode of operation and to de-energize the run mode power supply during the standby mode of operation. A typical switched mode power supply control IC normally has a start-up resistor connected to its supply voltage pin. The other terminal of the start-up resistor may be coupled either to the AC mains voltage or to a rectified mains voltage. The control IC needs to draw a current through the start-up resistor until an internal reference voltage is established within the control IC.
Disadvantageously, however, the control IC continues to draw current through the start-up resistor even after the internal reference voltage within the control IC has been established. This presents a problem because of the contribution by the power dissipated in the start-up resistor to the power consumed by the video display apparatus in the standby mode of operation.
The power consumed by electronic equipment in the standby mode is becoming an increasingly visible public policy issue. For example, an article in the Sep. 19, 1997, issue of Europe Energy reports that the European Commission regards reducing the energy consumed by electronic equipment in the standby mode of operation as a priority. The article further states that the Commission has concentrated its initial efforts at reducing the standby power consumption of televisions and VCRs, and that it has elicited voluntary commitments from manufacturers of such products to progressively reduce average standby power consumption to less than three watts.
It is therefore advantageous to reduce the power dissipated in the start-up resistor as one contribution toward the goal of reducing the power consumed by a video display apparatus, or other electronic equipment. Furthermore, as the standby power consumption is gradually reduced, it becomes even more advantageous to reduce the power dissipated by the start-up resistor because the power dissipated in the start-up resistor gradually becomes a greater percentage of the power consumed in the standby mode.
It is therefore desirable to provide a simple and cost-effective method for reducing the standby power consumption attributable to the start-up resistor of the switched mode power supply controller IC.